The present invention relates to a display device or more particularly to a display device having such an incomplete memory characteristic as that of ferrodielectric liquid crystal and which takes a specified time to rewrite the picture elements. The invention further relates to a driving system of the display device.
Ferrodielectric liquid crystal is a well-known element with incomplete memory characteristic. When a picture is to be displayed on a matrix type display panel that uses ferrodielectric liquid crystal, video signals are sent from, for example a personal computer to the display panel. Since the video signals from the personal computer are non-interlace signals, however, it is not possible to use all frames of the signals in displaying the picture on the panel because of the time restriction for rewriting by the ferrodielectric liquid crystal. Conventionally, therefore, a picture is displayed by using, for instance, every other frame of the video signals.
Assuming that the number of scanning lines M of a video signal sent from a personal computer is 200 and that the time required by the liquid crystal for rewriting the picture elements in one horizontal scanning period is 200 .mu.s, the frame frequency fF on the screen is calculated as: ##EQU1##
If the memory characteristic of the liquid crystal is incomplete, when a figure "1" is kept written, the luminance of the image changes little by little after the figure is rewritten, as shown in FIGS. 7(1), 7(2), 7(3) and 7(4). For instance, the luminance of the picture elements on the lines L.sub.1, L.sub.2, L.sub.3 and L.sub.4 changes as shown in FIGS. 7(1), 7(2), 7(3) and 7(4), respectively. The combined luminance of the 4 (vertical).times.4 (horizontal) picture elements changes at 25 Hz as shown in FIG. 7(5). Since human eyes can sense the luminance variation at a frequency not higher than 60 Hz, the above luminance change is sensed as a flicker so that the picture quality is deteriorated.